There are several different ways to set this up and hopefully someone with you exact same set-up can chime in. However, the short answer is yes. Unless your accessory battery is connected to it's own charger that runs off of a generator or dockside power it needs to be re-charged through one of the engines recharging system.
What leads are connected to it now.
Typically the system would have one motor lead (Positive) to the engine two battery.
The negative motor lead would be connected to the accessory battery negative terminal.
There would be a jumper lead from the negative terminal of the accessory battery to the negative terminal of the engine battery.
There would be a jumper lead from the positive terminal of the engine battery to the positive terminal of the accessory battery.
This set-up isolates battery one (Engine) from everything else so the accessories cannot drain it. However, engine 2 and the accessory (House) battery are wired parallel.
You need to follow all of the leads to see how it is wired because there are several different solutions to a 3 batt. system. As stated above, the charging lead could come off one of the batteries to the accessory battery switch (Assuming you have one). Star by isolating the battery 1 circuit. Then follow Batt. 2. GW usually wires the house to Batt. 1 so you may find the lead you are looking for there. Aftermarket set-ups can be wired any number of ways. Trace each circuit and you will find you missing lead.
